A number of medical conditions may be treated in a minimally invasive manner with various kinds of catheters designed to reach treatment sites internal to a patient's body. Balloon catheters, in particular, may be employed, for example, in angioplasty procedures, to widen obstructed blood vessels and optionally deliver stents; or in procedures to treat atrial fibrillation, such as by electrically isolating a patient's pulmonary veins. In some procedures, expansion of the balloon at the treatment site provides the desired therapy, such as expanding an obstructed blood vessel during an angioplasty procedure. In other procedures, an energy source within the balloon delivers the desired therapy, and the balloon serves to either position the energy source or communicate energy from or to tissue being treated. For example, in procedures for treating atrial fibrillation by electrically isolating pulmonary veins, a balloon catheter can be used to position a radio frequency energy source in proximity to the pulmonary vein tissue to be treated; similarly, in cryoablation procedures for treating the same condition, a cryotherapy balloon catheter can be used to extract heat, through the surface of the balloon, from the pulmonary vein tissue.